Spectroscopic Identification of Neurotoxin Tetramethylenedisulfotetramine (TETS) Captured by Supramolecular Receptorβ-Cyclodextrin Immobilized on Nanostructured Gold Surfaces

We report on the spectroscopic identification of tetramethylenedisulfotetramine (TETS), a deadly neurotoxic rodenticide, captured on plasmonic substrates using supramolecular guest-host functionality. Commercial nanopatterned surface-enhanced Raman spectroscopy (SERS) active substrates were self-assembled with hostβ-cyclodextrin (CD) and the captured TETS was readily identified by X-ray photoelectron (XPS) and infrared spectroscopy, but not with Raman. Density functional theory (DFT) calculation was carried out to determine the Raman scattering cross section of TETS to gauge its Raman scattering efficiency in the preresonant 633 nm excitation region. This was found to be lower than 10−29 cm2/sr, much lower than that of a dye molecule commonly used in SERS experiment. We explain the nondetection of TETS by Raman based on a combined intrinsically weak Raman scattering cross section and their low surface concentration, where XPS only shows a surface coverage of less than 0.02 monolayer with respect to the total number of gold sites. Comparing this to our own CD-decorated 10 nm gold nanoparticles (NPs) surface, we found that the inherently greater surface area provided by the NPs increases the amount of CD present (per unit area), giving our surface the capability to detect both the receptor and TETS via attenuated total reflectance (ATR) FTIR.